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View Code? Open in Web Editor NEW๐ฆ๐งฎ Arbitrary-length decimal library, implemented with ES2020's native BigInt.
Home Page: https://deno.land/x/bigdenary
License: MIT License
๐ฆ๐งฎ Arbitrary-length decimal library, implemented with ES2020's native BigInt.
Home Page: https://deno.land/x/bigdenary
License: MIT License
Hi,
I found an issue I want to highlight, curious about the position of the maintainer of this library on it.
I found that for bigdenary (100 / 3) * 3 != 100
and (100 / 3) + (100 / 3) + (100 / 3) != 100
the failing test are the following
Deno.test("BigDenary: (100 / 3) + (100 / 3) + (100 / 3) == 100", () => {
const b_d100 = new BigDenary(100);
const b_d33 = b_d100.div(3);
const b_d100sum = new BigDenary(0).add(b_d33).add(b_d33).add(b_d33);
assert(b_d100.eq(b_d100sum));
});
Deno.test("BigDenary: (100 / 3) * 3 == 100", () => {
const b_d100 = new BigDenary(100);
const b_d100mul = new BigDenary(100).div(3).mul(3);
assert(b_d100.eq(b_d100mul));
});
The tests succeed when a BigDenary is converted to number with valueOf()
, because valueOf()
internally convert to string and then uses parseFloat()
for the conversion to number, and because the converted string has more than 14 decimals, the returned number is rounded.
I decided then to test also decimal.js and number
object, and I found that: number
process them correctly (failing on others) while decimal.js
fails at them as this library.
Test file attached.
For completeness, I also tested C #, and using the decimal
type the problem is not present:
decimal d100 = 100;
decimal d33 = d100/ 3;
decimal d100sum = d33 + d33 + d33;
decimal d100mul = d33 * 3;
Console.WriteLine(d33);
Console.WriteLine(d100 == d100sum);
Console.WriteLine(d100sum);
Console.WriteLine(d100 == d100mul);
Console.WriteLine(d100mul);
Please take a look at https://deno.land/x/bigdenary
I think this line in the implementation is not safe it could cause rounding issues:
https://github.com/uzyn/bigdenary/blob/master/mod.ts#L31C7-L31C60
For example the following number will fail: 0.0023537
You can see the problem with this if you try the following calculation:
// 23536.999999999996 instead of 23537
0.0023537 * Math.pow(10, 7)
The response will be a float instead of an integer so it will fail with BigInt.
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